1. Field of the Invention
This invention relates to a sheet sorter and a method of controlling the sheet sorter, and more particularly to a sheet sorter which has a large capacity tray for receiving a large number of sheets discharged from an image forming apparatus such as a printer, a copier or the like without sorting the sheets and a plurality of sorting trays to which sheets discharged from the image forming apparatus are distributed after sorted and to a method of controlling the sheet sorter.
2. Description of the Related Art
As is well known, recent copiers are often provided with a sheet sorter mechanism. Such a copier is provided with a plurality of trays or bins which receive sheets discharged from the copier. The trays arranged in a vertical direction at suitable intervals. In some sheet sorter mechanisms, the trays are moved up and down simultaneously and in some sheet sorter mechanisms, the trays are moved up and down in sequence. In either case, a predetermined tray is brought to a sheet discharge port of the copier by the up and down movement, where the tray receives a sheet discharged through the sheet discharge port. By bringing a particular tray to the sheet discharge port according to the sort of sheet to be discharged, the sheets discharged from the copier can be sorted.
Generally the uppermost tray is used to stack sheets when the sheets need not be sorted and the sorter mechanism need not be operated. That is, when the sheets need not be sorted, all the sheets are discharged onto the uppermost tray. On the other hand, when the sheets are to be sorted, the second uppermost and the lower trays are used and are selectively brought to the sheet discharge port so that sheets are distributed to those trays by sort.
Some image forming apparatuses such as printers which output a large number of copies of the same sort are provided with a large capacity tray which accommodates one hundred or more sheets whereas said trays for sorting accommodate several tens of sheets at most.
Even for copiers, it is sometimes necessary to stack a large number of sheets on one tray and even for printers which output a large number of copies of the same sort, it is sometimes desired to sort sheets discharged therefrom.
An attempt at meeting such a requirement by enlarging the capacity of the uppermost tray in the known sorter mechanism for copiers described above will encounter the following difficulties. That is, since the sheet discharge port of the image forming apparatus must be positioned above a tray on which sheets discharged from the apparatus is to be stacked, the vertical distance between the bottom of the tray and the sheet discharge port must be much larger in the larger capacity tray, than in the sorting trays, in order to accommodate a large number of sheets. Accordingly, so long as the sheet discharge port is fixedly positioned, when the sheets are to be sorted, the maximum distance by which the trays are to be moved is determined by the sum of the height of the larger capacity tray and the height of the array of the sorting tray and becomes very large, which elongates the time necessary for moving the trays, enlarges the drive mechanism for moving up and down the trays and enlarges the overall size of the sorter.
Further when the sheets need not be sorted, the sheets are discharged onto the larger capacity tray even if the sheets are one or several in number. Since the larger capacity tray is generally provided with a high side wall in order to accommodate a large number of sheets, the high side wall interferes with taking out the sheets from the tray especially when the number of the sheets thereon is small.
Further when the sorter mechanism is to be operated, both the larger capacity tray and the sorting trays are moved up and down. Since the larger capacity tray is naturally large also in weight, a larger power is necessary to move up and down both the larger capacity tray and the sorting trays and the capacity of the drive motor must be larger.
Further when the sorter mechanism is operated, the uppermost sorting tray is first brought to the sheet discharge port and then the trays are moved upward pitch by pitch so that the lower sorting trays are brought to the sheet discharge port in sequence. Then when a predetermined number of sheets are discharged, the sorting trays and the larger capacity tray are moved downward so that the uppermost sorting tray is directly brought to the sheet discharge port. Thereafter the trays are moved upward pitch by pitch again. That is, the trays are moved intermittently overcoming the gravity. Since the drive motor requires a maximum torque when it starts rotating, to intermittently move upward the trays puts heavier load on the drive motor, which requires further larger capacity of the drive motor.